Tropical-Extratropical Interactions in a Hierarchy of Model Complexity

模型复杂性层次中的热带-温带相互作用

• 批准号: 1650209
• 负责人: Amy Clement
• 金额: $ 50.89万
• 依托单位: University of Miami
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-05-15 至 2021-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1650209&HistoricalAwards=false
• 关键词: Tropical; Extratropical; Interactions; Hierarchy; Model

Most weather systems in middle and high latitudes (the "extratropics") originate in the extratropics and are driven by extratropical processes, in particular temperature contrasts along fronts and the Coriolis force that compels winds to circulate around highs and lows. But extratropical weather systems can interact strongly with tropical weather and climate through a variety of pathways. One consequential example is atmospheric rivers (ARs), in which southerly winds in midlatitude systems produce narrow filaments of moisture extending from the tropics to the midlatitudes, where they produce heavy rain and flooding in regions such as coastal California. Another example is the Madden-Julian Oscillation (MJO), a large pattern of tropical precipitation and atmospheric circulation that forms in the Indian Ocean and propagates slowly eastward into the central tropical Pacific. The MJO has a variety of effects on midlatitude weather, including an increase in ARs along the US west coast and meanders of the jet stream that cause heat waves and cold air outbreaks. A key question for the MJO and for tropical-extratropical interactions on longer timescales is the role of air-sea coupling, as the importance of changes in sea surface temperature (SST) and subsurface ocean heat storage due to wind-driven evaporation is currently an open question.This project attempts to isolate the fundamental dynamics which drive the MJO, ARs, and slower variations known as meridional modes in which variability in the midlatitudes causes SST anomalies which propagate into the tropics over a year or two. The PIs develop and use a hierarchy of numerical model configurations at varying levels of complexity, in which the most complex configuration is used to realistically simulate the phenomena of interest. Progressively simpler model versions are used to reduce the complexity of the simulation so that the PIs can factor out non-essential details, allowing them to analyze the underlying dynamics in their simplest and most comprehensible form. For example, preliminary work shows that ARs can be produced in an "aquaplanet" model, in which the continents are replaced by ocean surface and SSTs are approximated as a simple function of latitude (warm near the equator and gradually cooling towards the poles). The simulation produces credible ARs despite the lack of continents, seasonality, and realistic SSTs, suggesting that the fundamental dynamics of ARs are best examined in simple models which lack these complexities.Models in the hierarchy are versions of the Community Atmosphere Model version 5 (CAM5), to which the PIs will add an aquaplanet version with "superparameterized" convection that is more appropriate for simulating the MJO, and two new representations of the ocean mixed layer. One version adds a simplified cooling rate calculation and relaxation to a specified temperature profile, a configuration which is sufficient to reproduce cold wakes behind tropical cyclones. The other is essentially the full physics mixed layer model from the Parallel Ocean Program, implemented in stand-alone columns at each ocean surface gridpoint. Comparisons between simulations with simpler and more complex mixed layers are used to understand the dependence of the MJO and meridional mode on the physics determining heat and moisture exchange between the ocean and overlying atmosphere.The work has scientific broader impacts through the development of the model hierarchy. The model versions developed in this project will be made available to the research community as part of the Community Earth System Model (CESM), which is hosted by the National Center for Atmospheric Research. They are part of an ongoing effort to developer simpler models using the CESM code base (which includes CAM5), and will be supported with documentation and reference simulations. More broadly, tropical-extratropical interactions are of societal as well as scientific interest due to their influence on US weather extremes.

中间和高纬度地区的大多数天气系统（“室外”）起源于室外，并由散热器过程驱动，特别是沿前部的温度对比，而coriolis力则迫使风在高高和低谷周围循环。 但是，热带天气系统可以通过多种途径与热带天气和气候强烈相互作用。 结果一个例子是大气河（ARS），其中中纬度系统中的南风产生狭窄的水分丝，从热带地区延伸到中纬度，在那里它们在加利福尼亚海岸等地区产生大雨和洪水。 另一个例子是Madden-Julian振荡（MJO），这是一种热带降水和大气循环的大模式，在印度洋形成，并缓慢地向东传播到热带太平洋中部。 MJO对中纬度的天气有多种影响，包括在美国西海岸的AR增加以及引起热浪和冷空气爆发的喷气流的蜿蜒。 MJO和在较长时间尺度上的热带 - 肢体相互作用的一个关键问题是空气耦合的作用，因为海面温度（SST）变化（SST）和地下海洋热存储的重要性是风向驱动蒸发引起的，目前是开放的问题。中纬度导致SST异常，在一两年的时间内传播到热带地区。 PI在不同级别的复杂性级别开发和使用数值模型配置的层次结构，其中最复杂的配置用于现实模拟感兴趣的现象。 逐渐简单的模型版本用于降低仿真的复杂性，以便PI可以分解非必需的细节，从而使他们可以以最简单，最可理解的形式分析基本动力学。 例如，初步工作表明可以在“水生膜片”模型中产生ARS，在该模型中，大陆被海面代替，而SST近似为纬度的简单功能（在赤道附近温暖并逐渐冷却杆）。 The simulation produces credible ARs despite the lack of continents, seasonality, and realistic SSTs, suggesting that the fundamental dynamics of ARs are best examined in simple models which lack these complexities.Models in the hierarchy are versions of the Community Atmosphere Model version 5 (CAM5), to which the PIs will add an aquaplanet version with "superparameterized" convection that is more appropriate for simulating the MJO, and two new representations of海洋混合层。 一个版本将简化的冷却速率计算和放松添加到指定的温度曲线上，这种配置足以再现热带气旋后面的冷唤醒。 另一个本质上是来自平行海洋程序的完整物理混合层模型，该模型在每个海面网格点的独立柱中实现。 使用更简单和更复杂的混合层的模拟之间的比较来了解MJO和子午模式对确定海洋和上覆氛围之间的热量和水分交换的物理学的依赖性。这项工作通过模型层次结构的发展具有更广泛的影响。 该项目中开发的模型版本将作为社区地球系统模型（CESM）的一部分提供给研究界，该模型由国家大气研究中心主持。 它们是使用CESM代码库（包括CAM5）开发更简单模型的持续努力的一部分，并将受到文档和参考模拟的支持。 更广泛地说，由于它们对美国极端天气的影响，热带 - 局部相互作用是社会和科学兴趣。

项目成果

Contributions of atmospheric and oceanic feedbacks to subtropical northeastern sea surface temperature variability

大气和海洋反馈对副热带东北海面温度变化的贡献

• DOI: 10.1007/s00382-019-04964-1
• 发表时间: 2019
• 期刊: Climate Dynamics
• 影响因子: 4.6
• 作者: Middlemas, Eleanor;Clement, Amy;Medeiros, Brian
• 通讯作者: Medeiros, Brian

Investigating the Influence of Cloud Radiative Effects on the Extratropical Storm Tracks

• DOI: 10.1029/2019gl083542
• 发表时间: 2019-07-16
• 期刊: GEOPHYSICAL RESEARCH LETTERS
• 影响因子: 5.2
• 作者: Grise, Kevin M.;Medeiros, Brian;Olson, Jerry G.
• 通讯作者: Olson, Jerry G.

Atmospheric Blocking and Other Large‐Scale Precursor Patterns of Landfalling Atmospheric Rivers in the North Pacific: A CESM2 Study

北太平洋登陆大气河的大气阻塞和其他大规模前体模式：CESM2 研究

• DOI: 10.1029/2019jd030790
• 发表时间: 2019
• 期刊: Journal of Geophysical Research: Atmospheres
• 作者: Benedict, James J.;Clement, Amy C.;Medeiros, Brian
• 通讯作者: Medeiros, Brian

Model Hierarchies for Understanding Atmospheric Circulation

• DOI: 10.1029/2018rg000607
• 发表时间: 2019-05
• 期刊: Reviews of Geophysics
• 影响因子: 25.2
• 作者: P. Maher;E. Gerber;B. Medeiros;T. Merlis;S. Sherwood;A. Sheshadri;A. Sobel;G. Vallis;A. Voigt;P. Zurita‐Gotor

Investigating the impact of cloud-radiative feedbacks on tropical precipitation extremes

• DOI: 10.1038/s41612-021-00174-x
• 发表时间: 2021-03
• 期刊: npj Climate and Atmospheric Science
• 影响因子: 9
• 作者: B. Medeiros;A. Clement;J. Benedict;Bosong Zhang